Senator Clinton proposed on February 27 more research funds for new energy technology, including “clean” coal systems. The next day, Mark Penn, her top campaign strategist, had a different take on coal.

In an internal blog at his other job, as chief executive officer of public relations firm Burson-Marsteller, Mr. Penn wrote of how Burson worked “behind the scenes” for TXU Corp., a Texas company seeking to build power plants fueled by pulverized coal, which some environmentalists say would be major polluters.

Contradictions between Mr. Penn’s private business dealings and Mrs. Clinton’s public policy positions — which Mr. Penn helps formulate and sell to voters — point up potential clashes in doing both campaign consulting and corporate advocacy. Mr. Penn’s firm works for clients, from a tobacco company to drugmakers, whose interests are often at odds with the New York senator’s agenda.

“That individuals and groups are serving today as both consultants to campaigns and as lobbyists or p.r. folks for private clients is a modern-day phenomenon that has inherent conflicts of interest,” the president of Democracy 21, a Washington-based group that advocates for tougher ethics laws, Fred Wertheimer, said. “It is a very unhealthy practice.”

Mr. Penn, 53, denies his work poses a problem. “I don’t think there’s any obligation that the firm’s clients agree on every issue that’s out there with either themselves or Senator Clinton,” he said in an interview Wednesday. “Lots of people have lots of disagreements, and that doesn’t make it a conflict.”

Mrs. Clinton’s campaign spokesman, Howard Wolfson, said Mr. Penn is currently working only with Microsoft Corp., a longtime client, and on the election campaign, although he’s free to handle and solicit other clients.

“The real question from the campaign perspective is whether Senator Clinton is comfortable with what Mark is doing, and the answer to that is yes, unequivocally,” Mr. Wolfson said.

Mr. Penn’s internal blog — several months of which were obtained by Bloomberg News — suggests that all along he has been working with multiple clients.

He downplayed his role in Mr. Clinton’s presidential campaign, saying he is “not a policy adviser, I’m a communications adviser.”

Others say he’s the most powerful figure in the campaign, and an April 30 Washington Post profile said he “has become involved in virtually every move that Clinton makes.”

Mr. Penn, who entered the top echelons of politics by helping President Clinton win re-election in 1996, sees no conflict, according to the blog, which he regularly writes for colleagues at the 2,500-person, New York-based Burson. In one entry, “Workin With Hillary,” he wrote, “I have found the mixing of corporate and political work to be stimulating, enormously helpful in attracting talent, and helpful in cross-pollinating new ideas and skills.”

“And,” he added, “I have found it good for business.”

Mrs. Clinton’s campaign owed Penn, Schoen & Berland Associates, the polling and consulting business Mr. Penn founded that’s now part of Burson-Marsteller, $277,147 for the first quarter of 2007.

Campaign consultants aren’t on the public payroll, so they’re not subject to the disclosure and ethics rules that apply to senior government employees. Thus, Mr. Penn’s blog offers a rare window into the strategic thinking of one of Washington’s top political operatives.

On March 23 of this year, he described a trip to Houston, where he met with John Hofmeister, the head of Royal Dutch Shell Plc’s American arm and a leader in an industry that Mrs. Clinton, 59, has criticized for reaping “windfall profits.”

Mr. Hofmeister is “interested in doing some more research around upcoming events — always good news,” Mr. Penn wrote.

In a blog entry last December 20, Mr. Penn touts the work Burson-Marsteller did to win an account with the U.S. Tuna Foundation, which was contending with federal warnings of elevated mercury in the fish. Burson pitched “ideas for how to act like a political campaign by neutralizing the negatives and bringing out the heart healthy benefits of tuna,” Mr. Penn wrote.

Mrs. Clinton, a Democrat, was one of 10 American lawmakers who signed an August 2004 letter criticizing then-Environmental Protection Agency Administrator Michael Leavitt for downplaying the mercury warning, which “specifically informs women that they and their young children should limit consumption of tuna.”

Among other Burson clients is Altria Group Inc., the New York-based successor company to Philip Morris Cos. As first lady in 1993, Mrs. Clinton banned smoking in the White House. Last year, she co-sponsored Senate legislation to force tobacco companies to stop advertising cigarettes as “light.”

Burson also represents Merck & Co. and Pfizer Inc., two of the largest companies in a pharmaceutical industry that’s opposed to a Clinton-backed proposal to allow the federal government to negotiate Medicare drug prices on behalf of consumers.

“On a wide range of policy issues, lots of people have lots of disagreements,” Mr. Penn said in the interview.

In the TXU case, company spokeswoman Lisa Singleton confirmed that Burson helped with its campaign to build 11 coal plants. She said TXU is “looking at clean-coal technologies and we have been all along.”

Mrs. Clinton isn’t the only candidate with advisers who have business interests. And the candidates themselves can choose to draw the line at the outside connections. President Bush, during his 2000 campaign, forced adviser Karl Rove to largely withdraw from a political consulting firm that had made him a millionaire. Philip Morris had been among his clients.

Still, few advisers have the range of outside interests or the prominent role in the presidential campaign that Mr. Penn does.

In his blog, Mr. Penn suggests he has used the access afforded by at least one major political client to woo business. In late January, he wrote that, thanks to an invitation by former client Tony Blair, Britain’s prime minister, he would be making his first trip to Davos, Switzerland, for an annual conclave of the world’s elite in business and government.

He hoped “to make it as useful as possible for Burson-Marsteller,” he wrote, ticking off planned meetings with executives from Visa International and Coca-Cola Co. Microsoft “rented an entire house right there, so they do Davos BIG,” Mr. Penn said in a later entry. At one point, “Bill Gates shook my hand, which is unusual … I missed Bono.”

Mr. Penn denied in the interview that he’s ever used his political connections to win business — including Mr. Blair’s invitation to Davos. “It’s inaccurate and false,” he said. “I’m sorry but being asked to a conference is hardly gaining access to clients,” he said. “You’ve turned this into an absurd game of gotcha.”

Mr. Penn was first ushered into the Clinton inner circle by consultant Dick Morris to help on Bill Clinton’s presidential campaign. Mr. Morris had to step aside after he was linked to a prostitute, and Mr. Penn moved into the void.

Mr. Penn co-founded Penn, Schoen & Berland in 1975 while still an undergraduate student at Harvard University, according to the company Web site.